The present invention relates to a magnetic disk apparatus, and more particularly, to a head support mechanism incorporating a microactuator for precise positioning of a magnetic head on a target track and a magnetic disk apparatus using the same.
With an increasing capacity of a magnetic disk apparatus in recent years, the magnetic head is required to perform extremely high precision positioning on a target track. Therefore, a drive mechanism has been proposed for a magnetic disk apparatus with a structure comprising a voice coil motor provided opposite to the magnetic head with respect to a carriage rotation center, which allows the magnetic head to move roughly, and an actuator for micro motion provided at a suspension.
For example, JP-A-11-16311 discloses a structure in which a micro actuator is provided between a load beam and a suspension provided with a magnetic head in addition to a coarse adjustment actuator.
Furthermore, JP-A-9-73746 discloses a head support apparatus comprising a head that performs data recording/reproduction on a disk that is driven to rotate and a plate-like elastic body having a first end and a second end. The head is mounted on the first end. The second end is provided with a load beam pivotally supported to move the head in a substantial radial direction of the disk, first and second piezoelectric thin films provided substantially in parallel to a longitudinal direction of the load beam on one surface of this load beam, third and fourth piezoelectric thin films provided substantially in parallel to the longitudinal direction of the load beam on another surface of the load beam and opposed to the first and second piezoelectric thin films, and first to fourth electrode pairs to apply voltage to the first to fourth piezoelectric thin films in their thickness direction, respectively.
In the above described prior art example, by applying voltage signals to the first to fourth electrode pairs so that, for example, the first and third piezoelectric thin films, and the second and fourth piezoelectric thin films expand and contract in phase, while the first and second thin piezoelectric films, and the third and fourth piezoelectric thin films expand and contract in inverse phase, high precision micro displacements for tracking compensation are given to the head.
For the microactuator, an electromagnetic type using a coil and a magnet has been conventionally considered, but recently a piezoelectric type using a piezoelectric element such as PZT is increasingly put into practical use from the standpoint of rigidity and manufacturing costs.
However, in the prior art structure with an entire piezoelectric element directly connected to a non-self-deforming plate-like load beam, the load beam constitutes large resistance against expansion and contraction of the piezoelectric elements. Thus, it is necessary to apply a voltage as high as 50V to the piezoelectric elements in order to move the head by 0.3 μm in the head positioning direction.
Furthermore, the piezoelectric element is made of a brittle member, and therefore it has disadvantages that it is vulnerable to impacts and sliding and is likely to produce dust from the sliding portion or portions on which stress is concentrated at the time of receiving an impact or at the time of driving the piezoelectric element. In the magnetic disk apparatus, a distance (flying height) between a flying side of the slider on which the magnet head is mounted and the disk surface is extremely small in the order of several tens of nm from the standpoint of improving the recording density. Therefore, if dust is produced, it becomes difficult to keep an appropriate flying height and it becomes impossible to perform the recording/reproduction. The slider or disk can be damaged in the worst case, leading to deterioration of reliability of the magnetic disk apparatus. Because of this, when using the piezoelectric element, there is a problem that it is necessary to eliminate the sliding portion and minimize stress produced when an impact is given from outside the magnetic disk apparatus or when the piezoelectric element is driven as small as possible.